Gas turbines in their stationary form have had their permanent place in power generation for a long time. In this case, it concerns high performance machines, the efficiency of which is constantly being further improved. An example of the stage of development which has been achieved are the type GT24/26 gas turbines of the Assignee of the present application, which are equipped with 2-stage sequential combustion, and which are described for example in the article by F. Joos et al., “Field experience with the sequential combustion system of the GT24/GT26 gas turbine family”, ABB review 5, p. 12-20 (1998). Inducted air is compressed in a compressor and fed to a first burner arrangement where it is used for the combustion of an injected fuel. This first burner arrangement comprises premix burners which among specialists have also been known as EV burners or possibly AEV burners. Such burners follow for example from EP-0321809 A1 and EP-0704657 A1 respectively, wherein these printed publications and also further publications which are related to this technology form an integrating element of this application. The hot gas which is created as a result of this combustion is first of all partially expanded in a high-pressure turbine and then introduced into a second burner arrangement (known among specialists as SEV burners), where the portion of unused air is used for a second combustion. The hot gas from the SEV burners is then expanded in a low-pressure turbine. The exhaust gases are then finally used for example for steam generation in a heat recovery steam generator.
On the outlet side of the SEV burner, the hot gas flow impinges upon the first row of stator blades of the low-pressure turbine. This configuration is described for example in U.S. Pat. No. 6,751,962 or in EP-A2-1 505 254, the contents of which are incorporated by reference as if fully set forth, and is reproduced in a detail in FIG. 1 of the present description. In the gas turbine 10 of FIG. 1, the hot gas 12, which discharges from the combustion chamber outlet 11, impinges upon the leading edge of the stator blades 15 of the first stator blade ring which is arranged at the inlet of the turbine. The combustion chamber outlet 11 is bounded at the side by means of a delimiting element 19. Between the end of the delimiting element 19 and the first stator blade row 15 there is a gap 16 which is sealed to the outside by means of an annular seal 17. By means of purging openings 18 in the seal 17 and leakages, purging air enters the gap 16 and prevents ingress of hot gas. Cooling air is also injected through cooling openings 20, 21 in the delimiting element, as is described in the aforementioned U.S. Pat. No. 6,751,962.
As a result of the fast flowing hot gas, various effects occur at the transition to the turbine. For one thing, a rearwards directed bow wave 13 is created at the leading edge of the stator blades 15, which is superimposed upon the pressure drops from the suction side 24a, 24b, 24c, 24d to the pressure side 25a, 25b, 25c, 25d. On the other hand, as a result of the complex flow conditions in the burners or combustion chambers with swirl elements which in most cases exist therein, a characteristic pressure distribution is created at the combustion chamber outlet 11, which can be referred to as a burner wave 14.
The unequal distribution of pressure at the combustion chamber outlet 11 in practice can be of the same order of magnitude as the pressure changes which ensue as a result of the bow wave 13 on the stator blades 15. The superimposition of the two effects (bow wave 13 and burner wave 14) can therefore lead to a situation in which the amplitude of the bow wave is effectively doubled and so hot gas escapes from the hot gas passage. These flow conditions, both in gas turbines with one combustion chamber or in gas turbines with sequential combustion, that is to say via 2 combustion chambers (EV, or AEV, and SEV), occur in each case at the transition from the burners to the turbine.